As resin compositions for encapsulation of optical semiconductors such as a light-emitting diode or for reflectors, epoxy resin compositions have been employed. As processes for producing the epoxy resin compositions, a process for continuously producing them at a good production efficiency has been proposed (for example, see Patent Document 1). The process uses a kneading apparatus shown in FIG. 2. Namely, in the kneading apparatus, a first kneader N1 having a heating unit H1 and a second kneader N2 having a cooling unit C1 are sequentially connected in series, supply ports 11 and 12 are formed at upstream parts of individual kneaders N1 and N2, and a discharge port 13 is formed at a downstream part of the second kneader N2. A mixture of a powdery epoxy resin and a liquid curing agent mixed previously is supplied from the supply port 11 of the first kneader N1 and the mixture is kneaded with a kneading screw S1 of the first kneader N1 while heating by a heating unit H1. By the kneading while heating, the mixture is homogeneously kneaded. Then, a kneaded product thereof is delivered to the second kneader N2. Subsequently, a powdery curing accelerator is supplied from the supply port 12 of the second kneader N2 and the kneaded product and the curing accelerator are kneaded by a kneading screw S2 of the second kneader N2 while cooling by a cooling unit C1. By the kneading while cooling, the curing accelerator is kneaded sufficiently and homogeneously with the kneaded product with suppressing the reaction of the epoxy resin with the liquid curing agent. Subsequently, the resulting kneaded product (epoxy resin composition) is discharged from the discharge port 13.    Patent Document 1: JP-A-2002-121261